The present invention refers to a new process for the fractionation of deacylated glycerophospholipids of the formula (I) ##STR3## wherein R is a negative charge, a hydrogen atom, a CH.sub.2 CH.sub.2 NR.sup.1 R.sup.2 residue (wherein R.sup.1 and R.sup.2, which are the same or different, are H or C.sub.1 -C.sub.4 alkyl), a CH.sub.2 CH.sub.2 N.sup.+ (CH.sub.3).sub.3 residue, a CH.sub.2 CH(NH.sub.2)COOH residue or a residue of the formula ##STR4## and X is OH or O.sup.-, starting from aqueous or hydroalcoholic mixtures, having two or more components, of said deacylated glycerophospholipids and of possible impurities of a non-glycerophospholipidic kind.
The process is characterized in that said mixtures are subjected to electrodialysis in electrolytic cells having a number of compartments, separated by cation exchange and/or anion-exchange membranes, in pH conditions suited to differentiate, depending on the positive, negative or neutral charge, the deacylated glycerophospholipids to be separated or other impurities of a non-glycerophospholipidic kind.
In the following description, the following abbreviations will be used:
GPA for the compound of formula (I) wherein R=H; PA1 GPE for the compound of formula (I) wherein R=CH.sub.2 CH.sub.2 NH.sub.2 ; PA1 GPC for the compound of formula (I) wherein R=CH.sub.2 CH.sub.2 N.sup.+ (CH.sub.3).sub.3 ; PA1 GPS for the compound of formula (I) wherein R=CH.sub.2 CH(NH.sub.2)COOH; PA1 GPI for the compound of formula (I) wherein R is a myoinositol residue. PA1 1) (-)cathode/catholyte/M.sup.- /compartment A/M.sup.+ /compartment B/M.sup.- /anolyte/anode (+) PA1 2) (-)cathode/catholyte/M.sup.+ /compartment C/M.sup.- /compartment A/M.sup.+ /anolyte/anode (+) PA1 3) (-)cathode/catholyte/M.sup.+ /compartment C/M.sup.- /compartment A/M.sup.+ /compartment B/M.sup.- /anolyte/anode (+) PA1 4) (-)cathode/catholyte/M.sup.+ /compartment A/M.sup.+ /compartment B/M/anolyte/anode (+) PA1 cathode: H.sup.+ +e.sup.- .fwdarw.1/2 H.sub.2 PA1 anode: 1/2 H.sub.2 O .fwdarw.1/4 O.sub.2 +H.sup.+ +e.sup.- PA1 MC 3470 (cation-exchange) and PA1 MA 3475 (anion-exchange) PA1 [Supplier CYBRON CHEM INC. (G.B.)] PA1 or PA1 CMT SELEMION (cation-exchange) PA1 AMR SELEMION (anion-exchange) PA1 [Supplier ASAHI GLASS CO. (J)] PA1 or PA1 CSP (cation-exchange) PA1 ADP (anion-exchange) PA1 [Supplier MORGANE (F)]. PA1 or PA1 NAFION 324 (cation-exchange) PA1 [Supplier DUPONT].
The compounds (I) may be of a fully synthetic origin or they may be obtained by deacylation, according to known methods, of acylated phospholipids of vegetal origin (e.g. soy lecithin) or of animal origin (e.g. egg yolk or bovine brain). In both instances, in the mixture of compounds (I) to be subjected to electrodialysis, impurities of a non-glycerophospholipidic kind can be present, which may be removed during the fractionation process or subsequently according to conventional techniques, such as crystallization, liquid/liquid extraction or chromatography.
The process surprisingly attains an effective fractionation of the compounds (I) using, in comparison with known methods, smaller amounts of chemical reagents or solvents, giving smaller amounts of waste to be disposed of, allowing to obtain compounds (I) with higher productivity.
Compounds (I) are characterized in that they may be positively or negatively charged or they may be electrically neutral according to the pH value of the solution. For instance, GPC is positively charged at pH values &lt;1 and amphotheric at pH values higher than 4, whereas GPE is positively charged at pH values &lt;1, amphotheric in the pH range from 5 to about 8 and negatively charged at pH values &gt;10. Similarly, such pH values of the solution can be found as to differentiate the species (I) in the mixture by means of the positive, negative or neutral charge. By the same method, it is possible to separate the compounds (I) from any other possible impurities in the starting mixtures.
Therefore, if a mixture of compounds (I), in aqueous or hydroalcoholic solution, is introduced at a suitable pH in a compartment of the electrolytic cell (hereinafter defined as compartment A), delimited by cation-exchange membranes and/or anion-exchange membranes, and an electrical potential is applied through the cell, it is possible to cause the migration of the negatively charged species to the anode through the anion-exchange membrane (having fixed positive charges and hereinafter referred to as M.sup.+) in an adjacent compartment (hereinafter referred to as compartment B), whereas the positively charged species migrate to the cathode through the cation-exchange membrane (having fixed negative charges and hereinafter referred to as M.sup.-) in an adjacent compartment (hereinafter referred to as compartment C) and leaving in compartment A the electrically neutral species.
According to the kind of mixture to be fractionated it is possible to carry out the separation working sequentially at different pH values.
The basic scheme of the cell, formed of a number of compartments, depends on the kind of mixture to be separated; in any case the electrodes, cathode and anode are present, in contact with electrolytic solutions of salts and/or inorganic acids or bases, respectively referred to as catholyte and anolyte, having a suitable composition and concentration compatible with the requirements of electrodic and fractionation processes. In compartments A, B and/or C, inorganic salts may also be present from the beginning or they may be subsequently added in order to increase conductivity whenever the presence of the charged species (I) would not be sufficient. The nature of the catholyte and anolyte is connected with that of the said inorganic salts, or to the kind of mixture of compounds (I) present in compartments A, B and C. The inorganic salts, acids or bases in the cell are dissociated in cations and anions and they may cross in their turn the membranes having opposite charge and they are repelled by the membranes having the same charge, competing in transport with the charged species (I). The compartments separated by the cationic and/or anionic membranes are in sufficient number to allow the introduction of the mixture of compounds (I) and the recovery of the fractionated species; the basic scheme may be repeated in series to increase the process productivity by connecting compartments of the same kind together.
For instance, cells of the following composition may be used:
For the sake of simplicity, the characterizing elements of these possible schemes of a cell are schematized, the inlets and outlets from and to the cell exterior having not been indicated.
Cells 1 and 2 are suited to the construction of a two-compartment stack, delimited by membranes of opposite sign as a repetive unit. Cell 3 is suited to the construction of a three-compartment stack, delimited by membranes of opposite sign. Cell 4 is suited to the construction of a more complex stack because of the membrane configuration, but it offers the advantage of securing a suitable conductivity even when the negatively charged species (I) have almost completely moved from compartment A to compartment B.
The process is characterized by the following electrodic reactions:
As a consequence, the electrodes conventionally used in electrolytic cells may be installed. Even simpler cells, having only one membrane (M.sup.+ or M.sup.-) are possible; in this case, the starting mixture and the fractionated species (I) are directly in contact with the electrodes. Therefore the fractionation conditions must be such that the species involved are stable with regards to the electrodic reactions, i.e. towards the development of oxygen and hydrogen. The membranes which can be used in this process are for example:
The cation-exchange membranes are permeable to the positively charged species (I) and to the inorganic cations present; the anion-exchange membranes are permeable to the negatively charged species (I) and to the inorganic anions present. Both kinds of membranes have good resistance to the operative pH values as well as mechanical and heat resistance, they are scarcely prone to clogging and they may be re-cycled after optional washings with water, with an hydroalcoholic solution, with a diluted acidic solution, with a diluted basic solution, again with water or with a saline aqueous solution according to the conventional method.
The starting concentration of the inorganic salts in the compartments ranges from 0 to 5M so as to obtain the best current density.
The process may be carried out at a current density from 20 to 3,000 A/m.sup.2, referred to the surface of each installed membrane. The following examples further illustrate the invention.